Dispersion producing method

ABSTRACT

A method for producing a dispersion of a dispersed phase in a continuous phase fluid in which the dispersed phase is immiscible. The method is performed in a system which includes a conduit containing a plurality of sheet-like elements extending longitudinally within the conduit. Each element is curved to turn the direction of fluid flowing past it. The elements are arranged in alternating right- and left- handed curvature groups (a group consisting of one or more elements). The two phases are injected into the conduit and pumped through it at predetermined velocity, which together with the density of the continuous phase, the interfacial tension between the phases and the inner diameter of the conduit determines the Weber number. The drop production reaches an equilibrium between break up and coalescence at about twelve elements and is well stabilized at 21 elements. The system and method can be used to extract solvents, remove color from or clarify liquids, remove or add heat, or affect mass transfer rates in reactions. It may completely oxidize a contaminant in an effluent, or for example, by dispersing an oxygen containing gas in water in which is disolved Na2SO3. Tests on various hydrocarbons dispersed in water are reported.

United States Patent Grout et al.

[ 1 DISPERSION PRODUCING METHOD [72] Inventors: Kenneth M. Grout,Topsfield; Richard D. Devellian, Rockport, both of Mass.

[73] Assignee: Kenics Corporation, Danvers, Mass.

[22] Filed: Jan. 25, 1971 [21] Appl. No.: 109,467

Primary Examiner-Walter A. Scheel Assistant ExaminerAla.n l. CantorAttorney-Russell & Nields [57] ABSTRACT A method for producing adispersion of a dispersed [451 Nov. 28, 1972 phase in a continuous phasefluid in which the dispersed phase is immiscible. The method isperformed in a system which includes a conduit containing a plurality ofsheet-like elements extending longitudinally within the conduit. Eachelement is curved to turn the direction of fluid flowing past it. Theelements are arranged in alternating rightand lefthanded curvaturegroups (a group consisting of one or more elements). The two phases areinjected into the conduit and pumped through it at predeterminedvelocity, which together with the density of the continuous phase, theinterfacial tension between the phases and the inner diameter of theconduit determines the Weber number. The drop production reaches anequilibrium between break up and coalescence at about twelve elementsand is well stabilized at 21 elements. The system and method can be usedto extract solvents, remove color from or clarify liquids, remove or addheat, or affect mass transfer rates in reactions. It may completelyoxidize a contaminant in an effluent, or for example, by dispersing anoxygen containing gas in water in which isdisolved Na SO Tests onvarious hydrocarbons dispersed in water are reported.

5 Claims, 9 Drawing Figures PATENTEDNMB I972 SHEET 1 BF 3 RIGHT-HANDLEFT- HAND F/G 30 761 3b FIG 36 F/G. 30

RICHARD p. DEVELLIAN BY asszfr9l lifls ATTORNEYS v SHEET 2 BF 3PATENTEDuuvea m2 ohm w; 009 oo. o

INVENTORS KENNETH M. GHQ-UT RICHARD D. DEVEL LIAN ATTORNEYS PATENTED 28I97? 3 704 O06 SHEETBUFS KENNETH M. GROUT RICHARD D. DEVELLIAN ATTORNEYSDISPERSION PRODUCING METHOD BACKGROUND OF THE INVENTION 1 Field of theInvention Method for producing a dispersion of a dispersed phaseimmiscible in a continuous fluid phase.

2. Description of the Prior Art The mixing or dispersion of one phase inanother with which the first is immiscible is important in many chemicaloperations such as heat and mass transfer. Dispersion not only bringsabout a large increase in the interfacial area available for suchtransfer but also places the two phases in a state of motion whichserves to increase the specific rates of the above transfer process.Dispersions may be classified by the rate at which the drops orparticles of the dispersed phase coalesce and separate from thecontinuous phase. When such drops or particles reach colloidal size sothat the dispersion becomes stable, non-settling and noncoalescing, thedispersion is termed an emulsion. However, the term dispersion" will beused herein its generic sense sense to include both stable andnon-stable distributions of drops or particles in a continuous fluidphase. Likewise, the term drops" will be used in the generic sense toinclude liquid drops, gas bubbles and solid particles.

Dispersions of one phase in another have been produced by injecting onephase in the other as a jet or sheet'whereupon surface tension forcescause the latter to collapse into a dispersion of drops. Fluiddispersions thus produced have been further reduced in drop size byshear or turbulent forces by pumping the dispersion through a pipe atvelocities which produce turbulent flow. Very high rates of fluid flowthrough orifices have produced dispersions by shear as the drops of thedispersed phase are propelled at high velocity through the continuousphase. Other mechanically driven agitators, stirrers and spinning diskshave also been utilized.

Demands of present technology have made it highly desirable to increaseefficiency and eflectiveness in the production of dispersions abovethose which the prior art affords. In addition, one important defect ofthe prior art is that the distribution of drop sizes has been undulywide. Ideally, particularly in chemical process, all drops should be ofthe same size and therefore each drop will have completed its chemicalinteraction with the continuous phase at the same time as each of theother drops. If there is a distribution of drop sizes about the idealdrop size, in general the larger drops will take too long to completetheir interaction and the smaller drops will have completed theirinteraction too soon. Likewise, particularly where the interactionrequires quite small drops which nevertheless are to be separated fromthe continuous phase when they have accomplished their purpose, theprior art has had a tendency to produce a substantial number of stillsmaller drops which make it very difficult to separate the dispersion byproducing coalescence of such drops.

In producing emulsions, it has been necessary to continue the process ofdrop subdivision for longer than is desirable in order to insure thatthe drops at the upper end of the drop size distribution shall becomesmall enough to come within the colloidal non-settling range.

SUMMARY OF THE INVENTION The present invention substantially reduces thelimitations of the prior art by producing the desired dispersion in amixer of the type described and claimed in the US. patent to Arrneniadeset al. US. Pat. No. 3,286,992. In this invention the mixer takes theform of a conduit containing a plurality of sheet-like elementsextending longitudinally within the conduit and each having a curvatureto turn the direction of fluid flowing past the element, the elementsbeing arranged in alternating rightand left-handed curvature groups (agroup consisting of one or more elements) and with the leading andtrailing edges of adjacent elements disposed at a substantial angle withrespect to each other. The two phases are injected into the mixer andforced to flow through it at a predetermined velocity which determines aWeber number, which in turn produces a predetermined Sauter mean dropdiameter of the dispersed phase. The invention may be used to extractsolvents, remove color from or clarify liquids, remove or add heat,affect mass transfer rates, or produce emulsions. A preferred embodimentis used to completely oxidize Na SO dissolved in effluent water.

BRIEF DESCRIPTION OF THE DRAWINGS In the annexed drawings:

FIG. 1 is a diagrammatic representation of a system incorporating oneform of this invention, with a portion of the mixer conduit broken away;

FIG. 2 is a perspective view of several of the elements used in themixer of FIG. 1;

FIGS. 3a, 3b, 3c, and 3d are some cross-sections taken through theconduit of FIG. 1 at the leading and trailing edges respectively of twoconsecutive elements;

FIG. 4 is a diagram showing a plurality of mixers of the type in FIG. 1connected in series:

FIG. 5 is a plot of the Weber number against the ratio between theSauter mean drop size and the inner diameter of the mixer conduit for aplurality of typical substances; and

FIG. 6 is a plot of the distribution in a typical case of drop sizesagainst total volume fraction of such drops.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, 10 is a hollow pipe,preferably cylindrical in cross-section, providing a conduit in whichthe dispersion of a material B of dispersed phase is to be produced in afluid material A of continuous phase. Within the pipe 10 is disposed aplurality of serially arranged curved sheet-like elements 11. A portionof pipe 10 is broken away to show several of such elements 1 1. It is tobe understood that any predetermined number of such elements may bepresent. Such number may be predetermined as will be explained below.Each of these elements is constructed of a flat sheet whose width mayequal the inner diameter of pipe 10 and whose length is preferably up toseveral times its width. Each element is so twisted that its upstreamand downstream edges are at a substantial angle to each other. Thisangle may vary between about 60 and 210. Also each successive element istwisted in the opposite direction with respect to its preceeding elementand the adjacent edges of successive elements are disposed at asubstantial angle, preferably with respect to each other. Instead ofreversing the twist of each successive element, a plurality of elementstwisted in one sense may be followed by a plurality of elements twistedin the opposite sense. Therefore, the elements may be considered broadlyas being arranged in alternating right-and left-handed curvature groups,it being understood that a group may consist of one or more elements.

Material A of the continuous phase may be introduced through a tube 12and pumped by a pump 13 through a tube 14 into a header 15 to which thetube is connected. Material 8 of the dispersed phase may be introducedinto the header through a tube 16 whereby it is injected into thecontinuous phase material A.

The velocity of the flow of the fluid mixture is determined by the flowof phase A which is regulated by the pump 13. The pump 13 may beelectrically driven and may have its speed determined by a speedregulator 17 of any well-known type. The regulator 17 may be calibratedin the velocity of fluid flow through conduit 10 or may even becalibrated in the Sauter mean drop size for the particular dispersioninvolved which may be determined as explained below.

When a fluid is caused to flow through the above structure with avelocity sufficient to produce a substantial dispersion of material B inmaterial A, the structure imparts a number of basic motions to theflowing material.

Firstly, the longitudinal flow of the liquid is reversed in the spiralpath which it follows through successive elements 11 as shown in FIG. 2in which the curved arrows designate the direction of flow. A secondtype of motion is illustrated in FIGS. 3a through which representsuccessive cross-sections through the pipe 10. FIGS. 3a and 3b are takenrespectively at the leading and trailing ends of an element 11 which istwisted in a left-hand direction. This causes the liquid flowing alongsaid element to spin within a clockwise direction so indicated by thearrows in said FIGS. FIGS. 30 and 3d are taken respectively at theleading and trailing ends of the element 11 following that shown inFIGS. 3a and 3b. The element 11 in FIGS. 3c and 3d is twisted in aright-hand direction and caused the liquid flowing along it to spin in acounter-clockwise direction as indicated by the arrows in FIGS. 3c and3d.

If we consider that the liquid emerges from the trailing end of eachelement 11 as two streams, we see that the leading edge of the followingelement 1 1 divides the liquid into double such number. While theidentity of each of the four resulting streams is substantiallydestroyed by the spinning action defined above, nevertheless the numberof such subdivisions increases exponentially according to the factor 2",where n is the number of sequential elements 11. Thus for 20 elements,over one million subdivisions are produced.

In addition, the point of maximum longitudinal velocity of flowconstantly changes with respect to the central axis of the tube 10 asthe fluid material moves through the structure.

The overall result of the above motions is that when the two immisciblefluids are caused to flow through the above structure, they aresubjected to very high shear stresses. particularly in each region wherethe spin of the fluid changes from one direction to another,

and drops of the discontinuous phase are produced within the continuousphase. As exemplified by the data reported below, it has been foundthat, in contrast with prior art devices, the efficiencies of theprocess of reducing average drop size, of narrowing the distribution ofthe sizes and generally or producing highly uniform and homogeneousdispersions are all substantially increased.

One series of tests conducted with the present invention involved thedispersion of the following liquids as the dispersed phase in water.These fluids and their physical properties are tabulated below, where prepresents density in grams per milliliter, p. represents viscosity incentipoises, and 0' represents the interfacial tension between the twophases in dynes per centimeter:

mo M P) 6 yne/ Anisole 0.99 l 26 Benzene 0.87 0.6 40 Benzyl alcohol I 55 Cyclohexane 0.76 0.8 46 Oleic Add 0.9 26 16 Toluene 0.87 0.6 32

The above properties are given at 25C.

The above materials were selected because they represent a range ofinterfacial tensions which is typical of most industrially importanttwo-phase systems. Also, variations in the density p and in viscosity p.for a wide variety of such industrially important systems will also liesubstantially in the range involved with the materials tested.

The tests included measurements of the sizes of the drops of thedispersed phase in a given volume of continuous phase from which theSauter mean diameter of such drops could be determined. The Sauter meandiameter, D7, is computed as SM 21nnD2 where n is the number of dropsobserved and D is the respective diameter of :each such drop. The Sautermean diameter .was determined because from it, and the volume fraction4: of the dispersed phase, the interfacial area per unit volume ofcontinuous phase a can be determined. The eflectiveness of any masstransfer process is directly dependent upon a The above quantities arerelated as follows.

v= fifi 4 In FIG. 5 is plotted the data obtained from the above listedmaterials using mixers of the type shown in FIG. 1. In FIG. 4, the Webernumber WE, computed as pointed out below is plotted against the value ofD /D-,- where D is the inner diameter of the tube 10. In each case 21elements 11 were used, each element having a pitch of 1.511. In one setof tests the tube 10 had an inside diameter of one-half inch and inanother set of tests, the tube 10 had an inside diameter of 1 inch.

The test demonstrated that the drop size or E; of the dispersed phase isprimarily controlled by the magnitude of the Weber number WE which isdefined as WE= .VD,/o- (a 3) where p is the density of the continuousphase, having an average longitudinal velocity V along a pipe or tubehaving an inner diameter of D and where ais the interfacial tensionbetween the two phases.

One of the most effective prior art devices for producing dispersions ina continuous flow process is a turbulent flow section of an empty pipeof sufficient length to produce the desired average drop size.Therefore, similar test were performed with comparable materials inempty pipes of the same internal diameter as those of the mixers used asdescribed above. The

results showed that, in order to achieve the same interfacial area inthe empty pipes, it is necessary to increase the Weber number by afactor of about 200. Since flow rate varies with the square root of theWeber number, this means that one needs to increase the flowrate in anempty pipe by a factor of about fifteen in order to obtain theinterfacial area that would be created in a mixer according to thepresent invention.

As the two phases A and B are introduced into the mixer, the elements 11break up the dispersed phase into drops which decrease in size as theflow progresses through the mixer. At the same time, some of the dropscoalesce into larger drops. After a certain number of elements have beenpassed, equilibrium is established between break up and coalescense atwhich point the minimum drop size is attained. Tests have shown that thenumber of elements at which such equilibrium is established issubstantially independent of velocity. The minimum number of elements atwhich such equilibrium is first attained is approximately twelve.Thereafter, as the flow continues through additional elements, suchequilibrium is maintained. As the flow passes beyond the last element ofthe system, coalescense continues without a corresponding break up andthe average drop size continues to grow until separation of the twophases is again complete. In view of the above, the number 21 wasselected as the number of elements in the tests reported above in orderto make sure that the minimum average drop size would be achieved ineach case.

The total number of elements actually usedin any system practicing thisinvention depends upon the degree to which the mass transfer process isto be carried out. Such process is time dependent and therefore asufficient number of elements are selected so that at the particularflow velocity involved, the average drop size will remain at its minimumvalue for whatever predetermined time may be required for such masstransfer process to proceed at its maximum rate. In a typical case, thenumber of elements may be as many as about 1,200, although manyapplications will require a much lower number. Where many elements areto be used, a plurality of such conduits 10 may be connected in seriesas shown in FIG. 4 where U-shaped headers 18 are used to join suchconduits in a compact folded arrangement. It is to be understood thateven after the flow leaves the last element, the mass-transfer processwill continue although at a decreasing rate as the average drop sizeincreases.

Another remarkable effect of drop size in dispersions produced inaccordance with this invention is that the drop size distribution issubstantially narrower than was previously attainable in related priorart systems. While the Sauter mean diameter is a characteristic measureof the drop sizes, it fails to give any indication of the range of sizesproduced. Various measurements were made of the distribution of dropsizes in dispersions produced in accordance with this invention. FIG. 6shows a typical distribution curve of data so determined, in which F,,,the total volume fraction associated with drops of a diameter less thansome maximum drop size D is plotted against the values of the actualdrop sizes measured. Thus, FIG. 6 represents a plot of the cumulativedistribution function. In the typical case illustrated in FIG. 5, itwill be seen that about 70 percent of the volume of the dispersion isassociated with drops whose diameter lies within 2 20 percent of theaverage drop diameter. As compared with the prior art, this is arelatively narrow distribution which greatly increases the effectivenessand efficiency in the production of dispersions by the presentinvention.

Dispersions may be produced by this invention for such purposes assolvent extraction, color removal or clarification, removal or additionof heat and to increase mass transfer rates in chemical reactions. Amongthe more common mixtures to which this invention is applicable are waterand hydrocarbons, and acidic or alkaline solutionsto be combined inorganic liquids. An important application of this invention is in theoxidation of oxidizable substances in effluents which have beencontaminating rivers, lakes and other bodies of water. The discharge ofsuch oxidizable substances causes a depletion of the oxygen content ofsuch bodies of water, often with a catastrophic effect on the ecologyinvolved. The efiectiveness of this invention in increasing the rate atwhich such substances may be oxidized in structures according to thisinvention is such that complete oxidation can be produced in reasonablysmall systems and with highly practical flow rates and powerconsumption. For example, stack gases from a combustion device whichcontain Na S0 may have the Na S0 dissolved in water. Thereupon thesolution is treated, in accordance with this invention, with a gasconsisting of or containing free oxygen as the dispersed phase in thewater as the continuous phase. Within a relatively compact andinexpensive structure, complete oxidation of the Na S0 occurs to produceNa S0 which makes no oxygen demand when the effluent is discharged andthus the efiluent becomes substantially noncontaminating. Otherimportant mass transfer processes, which will occur to those skilled inthe art, will be made possible by this invention.

What is claimed is:

l. The method of producing a dispersion of a first phase in a secondfluid phase, said phases being immiscible, which comprises:

a. injecting said phases into a conduit containing a plurality of curvedsheet-like elements extending longitudinally within said conduit andeach having a curvature to turn the direction of phases flowing throughsaid conduit, said elements being arranged in alternating rightandleft-handed curvature groups, the leading and trailing edges of adjacentelements in adjacent groups being disposed at a substantial angle withrespect to each other;

b. driving said phases through said conduit and past said elements at apredetermined velocity related to a Weber number which will producedrops of 3,704,006 ,7. said first phase having a corresponding Sauter 4.A method as in claim 1 in which said second fluid me n i me e1:- phaseis a liquid containing an oxidizable contaminent 2. A method as in claim1 in which said phases are d id fi t phase i a gas taini free oxygen.

caused to traverse a minimum of about 12 of said ele- A method as inclaim 1 in which Said second fluid ments arranged with alternateright-handed and left- 5 handed curvatures I phase is water having Na S0dissolved therein and said 3. A method as in claim 2 in which saidnumber of first phase ls agas coma'lmng free oxygen elements is aminimum of 21.

2. A method as in claim 1 in which said phases are caused to traverse aminimum of about 12 of said elements arranged with alternateright-handed and left-handed curvatures.
 3. A method as in claim 2 inwhich said number of elements is a minimum of
 21. 4. A method as inclaim 1 in which said second fluid phase is a liquid containing anoxidizable contaminent and said first phase is a gas containing freeoxygen.
 5. A method as in claim 1 in which said second fluid phase iswater having Na2S03 dissolved therein and said first phase is a gascontaining free oxygen.